1. Field of the Invention
This invention relates to method and apparatus for fixing one end of a boiler tube that is tightly retained in an aperture wall preparatory to pulling the tube during replacement thereof.
2. Description of the Prior Art
Tubes of relatively small diameter are widely used in boilers and in heat exchangers to increase the surface area across which heat is transferred during operation of such devices In the case of boilers there is typically a massive wall, and in heat exchangers there are two or more tube sheets; these walls or sheets are substantial permanent structures and are provided with numerous passages through which tubes of relatively small diameter are disposed. The tubes have a life that is shorter than the permanent structures in which they are installed so that replacement of the tubes at periodic intervals is common practice.
Because the tubes are tightly mounted within the passages, their removal is a non-trivial task. One technique that has been previously employed involves gripping the tube and applying sufficient longitudinal force to pull the tube from the passage in which it resides. As the tube slides along the passage, longitudinal striations are created in the passage surface; such striations form leak paths after installation of new tubes and consequent degradation of the efficiency of the device. In cases where a boiler wall or tube sheet is formed of alloys, pieces of the wall or tube sheet are liable to break away during such pulling so as to require replacement or extensive repair of the boiler wall or tube sheet.
The foregoing problems resulted in development of a technique that involves clamping the tube at one side of the boiler wall or tube sheet, gripping the other end of the tube, and applying tensile force to the tube. As the tube begins to fail, it elongates and reduces diameter so that when the tube finally fails in response to the tensile force, its diameter is sufficiently small that no damage is done to the portion of the boiler wall or tube sheet that defines the aperture or passage in which the tube is installed.
Typical practice requires two workers to effect removal of the tubes, one working on each side of the boiler wall or tube sheet. In addition to requiring more manhours, this prior art technique often requires access to virtually unaccessible chambers, in consequence of which great difficulty is experienced and the integrity of the portion of the boiler wall that defines the passage is jeopardized.